That's because this is obviously Arien's season. Season 1 was focused on both of their struggles. Season 2 is most likely about Arien's origins. Since it would be a mess if the story goes back and forth about their stories. Since they have different strengths. It's not like we can just ignore the fact on how important that her mother's blood is flowing stronger compared to her father's blood. There are a lot of things to tackle about that.
I'm sorry but since season 1 the spotlight have always been on Arien. Arjen have almost 0 moments and the story always focus on Arien side, thoughts and feelings. Arjen feel more like an accessory than an actual main character.
Just the fact that even him is overprotective of Arien and everyone talk about her and love her, she already has a harem but they met 0 girl their age. Arjen is clearly not the focus of the story, even when he is supposed to be more concerned like with the guardian, Arien is still the one that react stronger.
So far it's her story, not his.
finally dropping this if arien is the only mc when i like them both and it irks me that arjen's not gonna be on the spotlight